This section provides background information related to the present disclosure which is not necessarily prior art.
Internal combustion engines are used to generate considerable levels of power for prolonged periods of time on a dependable basis. Many such engine assemblies employ a supercharging device, such as an exhaust gas turbine driven turbocharger, to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency.
Specifically, a turbocharger utilizes a centrifugal gas compressor that forces more air and, thus, more oxygen into the combustion chambers of the engine than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the engine improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power.
A typical turbocharger employs a central shaft that is supported by one or more bearings and transmits rotational motion between an exhaust-driven turbine wheel and an air compressor wheel. Both the turbine and compressor wheels are fixed to the shaft, which in combination with various bearing components constitute the turbocharger's rotating assembly. Because the rotating assembly frequently operates at speeds over 100,000 revolutions per minute (RPM), the balance of such an assembly is essential for long term durability of the turbocharger.
With reference to FIGS. 5 and 6, a conventional turbocharger 100 is shown including a turbine 102 and a compressor 104 that are connected to one another by a central shaft 106. The central shaft 106 is supported by a pair of journal bearings 108, 110 which are each adjacent to one of the corresponding turbine 102 and compressor 104, respectively. The journal bearings 108, 110 are separated from one another by an annular spacer 112 disposed there between. Each of the journal bearings 108, 110 and the annular spacer 112 are received in a housing 114 of the turbocharger 100. With reference to FIG. 6, a perspective view of the journal bearings 108, 110 and spacer 112 are shown with the exterior surface of the journal bearings 108, 110 having a recessed annular groove 116 and an aperture 118 that are utilized for delivering lubricant from a lubricant passage in the housing 114 and to the interior space between the journal bearings 108, 110 and the central shaft 106. The grooves 116 and apertures 118 are optional depending upon the lubrication strategy since some lubrication systems supply lubrication to the journal bearings through a passage in the central shaft 106. The annular spacer 112 can be provided with holes 122 that are used as an anti-rotation feature on the spacer 112.